I feel like working on a challenging project for my next cosplay and I chose Tali, since I am currently engrossed with the game atm. Here's a link to a pic of her for those unfamiliar with the character. http://masseffect.bioware.com/universe/squad/tali/

I'd like to use a hard material for the armor parts and helmet. Is there any kind of easy to work with and cheap plastic that'll do?

And any tips on putting the swirls on the fabric, aside from fabric paint/pen?

fabric paint pen looks best if you have a steady hand. That's what I used for my Tali costume.

I just finished painting my Tali. This is the coolest looking method (did you use the silver lumiere paint too?), but it is MIND NUMBING and requires a steady hand and lots of patience. Set aside 2 weeks to slowly do it, lol. :P